The stock price rose 7.4 percent on Thursday, after initially declining on news its head of communications had been found dead.

The spokesman was under pressure over an investigation into alleged corruption and fraud that has rocked the world's oldest bank, reporters who knew him said.

The shares, which initially declined 2 percent, recovered after the lender said it would seek at least 1.2 billion euros ($1.56 billion) in damages from two former executives and investment banks Nomura and Deutsche bank over derivative trades that led to losses of around 730 million euros ($954 million).

David Rossi, born in 1961, was found dead at the bank's Siena headquarters on Thursday, lying beneath an open window overlooking a back street outside the building, a restored 14th century fortress.

Prosecutors in Siena are investigating whether Rossi, known as a reserved and serious professional, committed suicide, a judicial source said on Thursday.

"He was a very serious person, under pressure over a judicial probe which had touched on him through a recent police search, even if he was not under investigation," Andrea Greco, reporter at la Repubblica said on the newspaper's website.

"The death of David Rossi is a terrible tragedy," Monte dei Paschi said in a post on the bank's Facebook page, which carried a black stripe as a sign of mourning.

"This tragic event imposes first of all respect for his person, for the mourning of his family and for all of us, and calls on us to find the strength and the courage to go ahead and continue in our commitment."

Rossi, who was the head of the bank's communications unit, joined the Banca Monte dei Paschi di Siena's foundation, the bank's biggest shareholder, in 2001 as an assistant to then chairman Giuseppe Mussari.

When Mussari became chairman of the bank in 2006, Rossi remained his spokesman.

Rossi, who was not under investigation himself, was among several people whose homes and offices were searched last month as part of a probe into the lender's purchase of Antonveneta in 2007 and subsequent losses linked to complex derivatives deals.

"He surely lived through a situation of personal and professional stress," Greco said.

Mussari is under investigation in the probe on allegations of misleading regulators, market manipulation and false information in the prospectus of the Antonveneta deal.

"(David) was worried. We met on Thursday, he opened up a little, even though he was so reserved," David Taddei, a former partner of Rossi at a communication agency they founded in 1996, was quoted as saying in Il Corriere della Sera newspaper.